The oxygen- and iron-dependent sigma factor pvdS of Pseudomonas aeruginosais an important virulence factor in experimental infective endocarditis

In Pseudomonas aeruginosa, pvdS, a key oxygen (O-2)-dependent locus, regula tes expression of a number of virulence genes, including toxA (which encode s exotoxin A production). To define the in vivo role of differing O-2 tensi ons on pseudomonal virulence, 2 knockout mutants, Delta pvdS and Delta toxA , were compared with their parental strain, PA01, in rabbit aortic and tric uspid endocarditis models (representing aerobic vs. microaerobic conditions in vivo, respectively). In aortic endocarditis, Delta pvdS densities were significantly less than those of PA01 in vegetations, kidneys, and spleen ( P < .01). In contrast, in tricuspid endocarditis, there were no significant differences between Delta pvdS and PA01 tissue densities in these same tar get tissues. The Delta toxA mutant proliferated within target tissues to th e same extent as the parental strain. Thus, pvdS (but not toxA) appears to be required for optimal virulence of P. aeruginosa, particularly in tissues preferentially exposed to high O-2 tensions (e.g., aortic vegetations).